According to the U.S. Census Bureau, the county has a total area of 641 square miles (1,660 km2), of which 636 square miles (1,650 km2) is land and 4.4 square miles (11 km2) (0.7%) is water.[4] It is the fifth-smallest county in Washington by total area. It is part of the Palouse, a wide and rolling prairie-like region of the middle Columbia basin.

There were 8,364 households out of which 31.00% had children under the age of 18 living with them, 51.40% were married couples living together, 11.90% had a female householder with no husband present, and 32.40% were non-families. 27.00% of all households were made up of individuals and 11.70% had someone living alone who was 65 years of age or older. The average household size was 2.42 and the average family size was 2.91.

In the county, the population was spread out with 25.50% under the age of 18, 8.10% from 18 to 24, 26.10% from 25 to 44, 24.00% from 45 to 64, and 16.30% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 91.10 males. For every 100 females age 18 and over, there were 86.30 males.

The median income for a household in the county was $33,524, and the median income for a family was $40,592. Males had a median income of $35,810 versus $22,218 for females. The per capita income for the county was $17,748. About 11.60% of families and 15.40% of the population were below the poverty line, including 22.70% of those under age 18 and 6.70% of those age 65 or over.

This article is outdated. Please update this article to reflect recent events or newly available information.(November 2010)

Generally, Asotin County is considered a staunchly Republican area, although it has been known to vote for Democrats, especially on the state level. Currently the county is represented at the county level by two Democrats and one Republican.

In 2004, 27% of presidential votes were cast from incorporated Clarkston, while 61% was from unincorporated suburbs of Clarkston (34% from Clarkston Heights, 12% from West Clarkston, 9% from South Clarkston, and 6% from Swallows Nest). An additional 6% was cast from the incorporated city of Asotin, with rural areas around Asotin accounting for 4% of the vote and areas around the unincorporated community of Anatone making up 2% of the vote.

By and large, the most competitive areas are Clarkston and its suburbs. Democratic presidential nominee John Kerry won two precincts in 2004, one each in Clarkston and West Clarkston. Bush received 54 percent of the vote in West Clarkston, 55 in Clarkston, and 57 percent in South Clarkston. However, he received larger victories of 64 percent in Clarkston Heights and 67 percent in Swallows Nest. Areas around both Asotin and Anatone delivered 2-to-1 victories, with the lone exception of one of the two incorporated Asotin precincts.